1. Field of the Invention
The present invention relates to a work or component mounting apparatus for mounting an IC chip or some other electronic component, as a work, on a printed board.
2. Description of the Related Art
As used herein, "work" is utilized to denote a component, such as an electrical component, which is retrieved from a supply and mounted upon a mounting surface such as a printed board by a work mounting apparatus. Thus, as should be readily recognized, work is utilized interchangeably with component, with a work mounting apparatus denoting an apparatus which mounts a component upon a device or an element of a device.
A work mounting apparatus of this type is disclosed in Published Unexamined Japanese Patent Application No. 62-114290, for example. This conventional apparatus comprises a rotating table and a plurality of suction heads arranged at predetermined intervals on the outer peripheral edge of the table. Each suction head is capable of up-and-down motion.
A workbench is disposed under the rotating table, and a work (or component) supply section and a work (or component) mounting section are arranged on the workbench at a distance from each other in the circumferential direction of the table. A plurality of work feeders are radially arranged in the supply section, while a printed board is disposed in the mounting section.
When one of the suction heads is positioned in one of the work feeders of the supply section as the table rotates, the rotation of the table is stopped. In this state, the suction head is lowered, receives a work from the work feeder by suction, and is then raised to its original position. When the rotation of the table is restarted, thereafter, the suction head is transferred from the supply section to the mounting section. When the suction head is positioned in the mounting section, the rotation of the table is stopped again. In this state, the suction head is lowered again, whereupon the work is released from the suction, so that it is mounted on the printed board in the mounting section.
According to the work mounting apparatus described above, the rotation of the table must be stopped every time the suction head is moved up or down, that is, every time the work is received or mounted in the supply or mounting section. In other words, the rotation of the table and the operation of the suction head are performed intermittently, so that the tact time cannot be shortened, and therefore, the work mounting efficiency is low.
In these circumstances, there is a demand for continuous-type work mounting apparatuses in which works can be received and mounted without stopping the rotation of the table.
In one such continuous-type mounting apparatus, for example, a continuously rotatable drum, which is used in place of the rotating table, is surrounded by a plurality of work heads which repeat up-and-down motion as they turn. More specifically, the work heads turn around a turning axis which extends in the radial direction of the rotating drum, and their respective postures are kept fixed during the turning motion.
Thus, if a suction nozzle is provided protruding downward from each work head, it can repeat up-and-down motion while moving in the circumferential direction of the rotating drum, as the drum rotates and as the work head turns.
If the turning speed and turning direction of the work head are properly set with respect to the peripheral speed of the rotating drum, moreover, the relative speed of the suction nozzle with respect to the supply and mounting sections, that is, the ground speed, can be reduced substantially to zero when the suction nozzle lowers so that the supply and mounting sections come closest to each other. Even while the rotating drum is being continuously rotated, therefore, the suction nozzle of the work head can securely receive a work from one of the work feeders of the supply section by suction, and then mount the received work head on a printed board in the mounting section.
In the continuous-type work mounting apparatus described above, the suction nozzle is supplied with suction pressure and attracts a work at its distal end, and therefore, the distal end of the nozzle must be capable of close contact with the work. Namely, if the distal end of the suction nozzle incompletely contacts the work when the work is attracted to the nozzle, then the suction pressure acted upon the work becomes insufficient and the work cannot be reliably attracted to the nozzle.
In the course of long-term repetition of suction and mounting of works, however, the distal end of the suction nozzle is worn away, which is an unavoidable phenomenon. In other words, the suction nozzle is an expendable part that requires regular replacement. Moreover, depending upon the types of works, replacement of the suction nozzle is required regardless of whether the nozzle has been used up to its limit of durability.
When replacing the suction nozzle, first, the work head must be detached from the drum. It is, however, difficult to detach the work head. Namely, the work head and the rotating drum side are connected to each other not only by a mechanism for turning the work head but also a mechanism for keeping the work head in a fixed posture during the turn of the work head. Thus, first of all, these mechanisms must be disassembled before detachment of the work head.
To cause the suction nozzle to carry out suction and mounting of works, the supply of the suction pressure to the suction nozzle must be controlled, and such control essentially requires the use of a solenoid-operated value, a controller for controlling the shifting of the valve, and the like.
If the solenoid-operated valve, controller, and related parts are arranged in the rotating drum, the path of transfer of a shift signal from the controller to the solenoid-operated valve can be advantageously simplified. In this case, however, the rotating drum is increased in size and the internal arrangement thereof becomes complicated. Thus, difficulty arises not only in the assembling of the drum but also the maintanance of the electrical system. Further, it is difficult to arrange the parts in the drum such that the weight of the drum is well-balanced in the circumferential direction thereof, and thus, smooth rotation of the drum cannot be achieved.